Heating the Sun’s Corona
The temperature at the surface of the sun is 6000 kelvin, but the temperature of the sun’s corona is more than 3,000,000 kelvin. But it is still a mystery how the sun’s corona is heated to such a high temperature.
Much of the the 7 December 2007 issue of Science is devoted to the Hinode (“sunrise”) solar space telescope mission. (The web site for the mission is in Japanese, if you read that language.) Hinode was launched in September 2006 and since October 2006 has observed the sun from earth orbit. The initial observations have provide clues for solving the mystery of heating the sun’s corona.
In a perspective, Erdélyi and Fedun (p. 1572) explain that there are at least three fundamental questions to be answered.
Where is the energy generated? How does the generated energy propagate from the energy reservoir to the solar corona? How does the transported energy dissipate efficiently in the solar corona to maintain its multimillion-kelvin temperature?
It is now clear that the powerful magnetic fields in the solar atmosphere play a crucial role in heating the corona. In 1970, Hannes Alfvén was awarded the Nobel prize in physics for his predictions of magnetic waves, now called Alfvén waves, in the solar atmosphere. Many of Hindode’s observations are consistent with the presence of Alfvén waves, and the waves are sufficiently powerful to generate the solar wind and heat the corona.
February 29 2008 09:25 pm | Astronomy
